The present invention relates to motor vehicle crash discrimination systems utilized for actuating or deploying a passenger safety restraint, and more specifically to apparatus and method for improving reliability of a motor vehicle crash discrimination system.
Conventional vehicle crash discrimination systems typically employ at least one mechanical, electromechanical, or electronic acceleration sensor affixed to the vehicle for sensing vehicle acceleration. The output of the sensor(s) are supplied to a discrimination circuit for comparison to a predetermined threshold value. If the predetermined threshold value is exceeded, the discrimination circuit will output a signal which actuates or deploys a passenger safety restraint, such as an airbag or passive seat belt mechanism.
However, conventional mechanical or electromechanical accelerometer based crash discrimination systems do not account for variations in passenger/occupant conditions in determining whether to actuate the safety restraint. More specifically, conventional accelerometer based crash discrimination systems are generally designed to assume nominal conditions, such as 50th percentile male, actual presence of a vehicle occupant, and failure of an occupant to wear a seat belt. The assumption of these crash conditions are necessary to insure proper actuation of the safety restraint when severe deceleration of the vehicle is detected by the accelerometer. Such assumptions inherently cause unnecessary, undesired, or improperly-timed actuation of the safety restraint in conditions where no occupant is present, in marginal crash situations where a seat belt provides sufficient safety protection for the occupant, or in situations where the occupant is improperly positioned relative to the safety restraint such that actuation of the safety restraint could potentially injure the occupant.
Further, each type of vehicle structurally reacts in a unique manner when experiencing identical crash situations. Since conventional accelerometer based crash discrimination systems detect crash situations based on deceleration of the vehicle, the accelerometer must be specifically calibrated for the particular type of vehicle to which it will be mounted. The requirement of unique calibration adds to the cost and complexity of conventional accelerometer based crash discrimination systems.
Another known vehicle crash discrimination system disclosed in U.S. Pat. No. 5,118,134 to Mattes et al measures both the forward displacement and/or velocity of vehicle occupant, and the acceleration of the vehicle in determining when to actuate a safety restraint. The forward displacement or velocity of the occupant is measured using ultrasonic, light or microwave signals. The vehicle acceleration is compared to a first threshold value, the forward displacement of the occupant is compared to a second threshold value, and the velocity of the occupant is compared to a third threshold value. The safety restraint is actuated when the first threshold value is exceeded, and either the second or third threshold values are exceeded.
While the system disclosed in U.S. Pat. No. 5,118,134 improves reliability over conventional accelerometer based crash discrimination system by measuring occupant displacement or velocity, the system is still relatively rigid because of the use of preset threshold values as the decisional criteria for actuating the safety restraint. This arrangement does not allow the crash discrimination system to accommodate various occupant conditions which can affect the desirability of actuating the safety restraint.